1. Field of the Invention
This invention relates to improvements in a double overhead camshaft engine in which intake and exhaust valves are operated by two camshafts, and more particularly to a camshaft driving device including an idler gear through which the camshafts are driven by a crankshaft of the engine.
2. Description of the Prior Art
A variety of camshaft driving devices for double overhead camshaft engines have been proposed and put into practical use. One of these devices is disclosed, for example, in Japanese Patent Provisional Publication No. 60-50208, in which two camshafts are driven by a crankshaft of the engine through an idler gear for deceleration and drive chains. Here, the idler gear is rotatably mounted on an idler gear installation bolt which is disposed bridging the front end section of the cylinder head and a cover disposed independent and spaced from the cylinder head front end section.
Thus, in the above conventional camshaft driving device, the idler gear installation bolt is supported in bolt holes in the cylinder head front end section and in the cover. Therefore, the following difficulties have been encountered in the conventional camshaft driving device, in which the bolt holes for the idler gear installation bolt in the cylinder block front end section and the cover become eccentric with each other under thermal deformation of the cover and by assembly error of the camshaft driving device. This causes oil leak from the bolt hole in the cover. Additionally, the cover obstructs the operator's ken during assembly of the idler gear in the camshaft driving device, so that positioning between the timing marks of the idler gear and a drive chain becomes difficult thereby causing disorder in opening and closing timings of intake and exhaust valves.